Maintaining synchronization of multiple data channels with a common clock signal

ABSTRACT

Maintaining synchronization when sending/receiving multiple channels of data with a corresponding common reference clock signal. Synchronization signals (e.g., pulses) are generated periodically and the timing of channels is adjusted. In an embodiment, multiple sequences of parallel data elements are received on corresponding parallel data channels using a first common clock signal. Each sequence of parallel data elements is converted to a corresponding sequence of serial data elements. The serial data elements are transmitted on a corresponding serial channel using a serial clock as a common reference. A synchronization signal may be generated periodically with a time period of (the number of bits in each parallel data element x the time period of the serial clock), wherein ‘x’ represents multiplication operation. As the parallel data channels are synchronized in short intervals, synchronization is maintained.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to communication systems, and morespecifically to a method and apparatus for maintaining synchronizationof multiple data channels to a common clock signal over time.

2. Related Art

Channels are often provided using various types (e.g., wire-based,wire-less, etc.) of paths, and are used to transfer data. A clock signaloften provides a time reference for the data transfers such that thedata can be recovered at the receiving end using the time reference.

Data is often received on one channel (“receive channel”) andtransmitted on another channel (“transmit channel”). Data streams areoften received on corresponding receive channels, and each data streamis transmitted on a corresponding transmit channel.

It is often desirable to synchronize multiple data channels to a commontime reference. Such a synchronization may enable, for example, a commonclock signal to be used supporting the transfer of data on all the datachannels. By using a single reference signal, several advantages such asminimizing a number of pins, minimizing electrical power consumption,etc., can be obtained, as is well known in the relevant arts.

One problem often encountered is that data channels may goout-of-synchronization over a long period of operation (e.g., due toalpha particles hits, power supply glitches, or drift), even if thechannels are synchronized at some point of time. The absence ofsynchronization may lead to errors in transmission and/or reception ofbits as is well known in the relevant arts, and is thereforeundesirable. Accordingly, at least for such reasons, it may be desirableto continue to maintain synchronization of the data channels such thatthe data may be reliably sent and/or received.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, synchronization signals(e.g., pulses) are generated with a short interval, and the generatedsynchronization signals are used to re-synchronize any parallel datachannels, which are out-of-synchronization (“out-of-sync”), to a commontime reference. By re-synchronizing the out-of-sync at short intervalsto the common time reference, synchronization may be continued to bemaintained over a long period of time. Such continued synchronizationmay enable a common clock signal to be used as a reference signalassociated with all the parallel data channels. Using a common clocksignal may result in several advantages such as reduction of electricalpower consumption.

In an embodiment, a transmitter block contains a synchronizationgenerator and multiple converter blocks. The synchronization generatorgenerates a sequence of synchronization signals with a short interval.Each converter block receives a sequence of parallel data elements(e.g., bytes) on a corresponding parallel data channel using a firstcommon clock signal, and converts the parallel data elements to acorresponding sequence of serial data elements (bits). The converterblock sends the sequence of serial data elements on a correspondingserial data channel.

The converter blocks receive the synchronization signals and ensure thatall the parallel data channels are synchronized to a common timereference in response to a synchronization signal. In an implementation,each parallel data contains a byte (8 bits) and the synchronizationsignals are generated periodically with a time period of eight times thetime period of a second clock signal used as a common clock referencefor the serial data channels.

An embodiment of the transmitter block is used to implement an OC-192(10 GBPS) node. The embodiment may contain 16 converter blocks, witheach converter block operating at 622.08 Mbps.

Each converter block may contain a shift register converting eachparallel data element into serial data elements, with the shift registerloading each parallel data element at a time point specified in relationto a synchronization signal. The shift register shifts a loaded paralleldata element to generate corresponding serial data elements. In anembodiment, the converter block contains a sync counter generating aselect signal synchronized with the synchronization signals, wherein theselect signal specifies the time point to load each of the parallel dataelements in the shift register. The sync counter may further generatethe first common clock signal synchronized with the synchronizationsignals.

The transmitter block may further contain a PLL (phase lock loop)generating a PLL clock signal, and a signaling circuit passing the PLLclock signal as the second common clock signal when a reset signal isnot received. The signaling circuit venerates the second common clocksignal and a complement of the second common clock signal, which areout-of-phase by 180 degrees, wherein the shift register is coupled toreceive the second common clock signal and the complement of the secondcommon clock signal. The signaling circuit further synchronizes thereset signal to the PLL clock signal to generate a clear signal, whereinthe clear signal causes the shift register to be cleared to all zerosstate.

A receiver block may also be implemented using several of the approachesnoted above. The receiver block receives serial data channels and sendsthe data in corresponding parallel data channels. Synchronizationsignals may be used to synchronize the parallel data channels to acommon time reference, and a common clock may be used to support all theparallel data channels. Such use of a common clock signal again leads toseveral advantages such as reduction of power consumption requirements.Embodiments of the transmitter block and receiver block may beimplemented, either individually or in combination, in severalenvironments such as SONET networks.

Further features and advantages of the invention, as well as thestructure and operation of various embodiments of the invention, aredescribed in detail below with reference to the accompanying drawings.In the drawings, like reference numbers generally indicate identical,functionally similar, and/or structurally similar elements. The drawingin which an element first appears is indicated by the leftmost digit(s)in the corresponding reference number.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described with reference to theaccompanying drawings, wherein:

FIG. 1 is a block diagram of an example system in which the presentinvention may be implemented;

FIG. 2 is a flowchart illustrating the details of a method by whichsynchronization may be maintained in various data channels according toan aspect of the present invention;

FIG. 3 is a block diagram illustrating the details of a receiver in anembodiment of the present invention;

FIGS. 4A through 4C together depict a circuit diagram illustrating thedetails of a serial to parallel converter in an embodiment of thepresent invention;

FIGS. 5A to 5C are graphs together illustrating the manner in whichvarious clock signals are synchronized according to an aspect of thepresent invention;

FIG. 6 is a circuit diagram illustrating the details of a sync generatorin an embodiment of the present invention;

FIG. 7 depicts a table illustrating the details of eight states reachedby a sync generator in an embodiment of the present invention;

FIG. 8 is a block diagram illustrating the details of a transmitter inan embodiment of the present invention;

FIG. 9 is a circuit diagram illustrating the details of an embodiment ofa parallel to serial converter used in a transmitter; and

FIG. 10 depicts a table illustrating the details of eight states reachedby a sync counter in a parallel to serial converter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

1. Overview and Discussion of the Invention

An aspect of the present invention generates synchronization (sync)signals which are used to synchronize multiple parallel data channels toa common time reference. The sync signals may be generated periodicallyat short intervals and any parallel data channels which areout-of-synchronization may be re-synchronized upon receiving a syncsignal. By maintaining synchronization, a common clock signal may beused associated with all the parallel data channels.

Several aspects of the invention are described below with reference toexamples for illustration. It should be understood that numerousspecific details, relationships, and methods are set forth to provide afull understanding of the invention. One skilled in the relevant art,however will readily recognize that the invention can be practicedwithout one or more of the specific details, or with other methods, etc.in other instances, well-known structures or operations are not shown indetail to avoid obscuring the invention.

2. Example Device

FIG. 1 is a block diagram containing device 100 receiving andtransmitting data on SONET network 135. Device 100 is shown containingline card 125 and switch fabric 130. Line card 125 receives high speeddata (e.g., at 10 GBPS) on path 101. Switch fabric 130 receives the datafrom line card 125 and forwards the data in the form of frames to thecorresponding end systems (not shown). Similarly, device 100 receivesframes from the end systems and sends the corresponding data on path101, for eventual transmission on network 135.

Line card 125 is shown containing SERDES (serializer-deserializer) 10and framer 120. For illustration, it is assumed that the interfacebetween SERDES 110 and framer is implemented to support SFI-4 112(SERDES Framer Interface-4) standard defined by Optical InternetworkingForum (OIF). However, device 100 can be implemented with other standardsand other environments as well. SFI-4 standard is described in furtherdetail in a document entitled, “OfF-SFI4-01.0—Proposal for a commonelectrical interface between SONET Framer and serializer/deserializerparts for OC-192 interfaces”, available from http://www.oiforum.com/,and is incorporated in its entirety into the present application. Eachcomponent is described below first with respect to receiving data fromnetwork 135 and then with respect to transmission.

Continuing with respect to reception of data from network 135, SERDES110 receives serial data on path 101 and may provide the same data usingmultiple (more) serial data channels on path 157 to framer 120. By usingmore channels, the data may be provided using a slower clock signalcompared to a clock signal used to receive data on path 101. In anembodiment, SERDES 110 may provide the data received (using potentially4 channels) on path 101 over 16 data channels on path 157. Thus. SERDES110 converts the high speed data received on path 101 into lower speeddata by using more channels on path 157.

Framer 120 may convert the data received in each channel tocorresponding frames (e.g., IP packets), and the frames are forwarded toswitch fabric 130 on path 193. The conversion may be performed in aknown way.

Similarly, with respect to transmission of data to network 135, framer120 receives frames on path 193, and converts the frames into a formsuitable for transmission on network 135. The converted data for eachframe is assigned to a corresponding serial data channel, for example,based on user configuration. The resulting multiple (16 in theillustrative example) serial data channels are provided on path 186.

SERDES 110 may receive the data corresponding to 16 channels on path 186and provide high speed data on path 101. SERDES 110 is shown containingSERDES core logic 140, transmitter 150 and receiver 160. Each componentis described below.

SERDES core logic 140 may receive high speed serial data on path 101 andconvert the high speed serial data into low speed parallel data on path145. In the illustrative example of optical carrier-192 (OC-192) havinga throughput of 10 Gbps. SERDES core logic 140 may receive 3.125 Gbpsserial data on four channels over path 101. The same data is convertedinto 16 channels, with each channel containing parallel data of eightbits each. Such conversion from serial to parallel data for each channelmay be performed in a known way.

Thus, SERDES core logic 140 may provide 128 bits of data to transmitter150 during each clock cycle (assuming 8 parallel bits of data arepresented for each of the 16 channels). Accordingly, transmitter 150 mayreceive data bytes using a clock signal with a lower frequency comparedto the frequency at which bits are received on path 101. Similarly,SERDES core logic 140 may also receive low speed parallel data on path164 and may convert the parallel data into higher speed serial data onpath 101.

Transmitter 150 may receive the low speed parallel data on path 145 foreach parallel data channel and provide the corresponding higher speedserial data channel on path 157. In the illustrative example,transmitter 150 may use 16 serial data channels on path 157 to supportthe corresponding 16 parallel data channels. Each of the 16 serial datachannels may operate at a clock frequency of 622 Mbps. As described insections below, a common clock signal may be used associated with allthe 16 parallel data channels, another common clock signal may be usedassociated with all the 16 serial data channels.

Receiver 160 receives data on multiple serial data channels on path 186using a common clock signal. The data corresponding to each serial datachannel may be converted into parallel data (e.g., bytes) and providedon path 164 using a slower clock signal compared to the common clocksignal received on path 186. In the illustrative example, path 164 maycontain 128 bits (in addition to other paths for purposes such asclocking) corresponding to a byte of parallel data for each of the 16channels.

Framer 120 is shown containing receiver 170, transmitter 180 and framercore logic 190. Each component is described below.

Receiver 170 may receive high speed serial data for each of multiplechannels on path 157 and provide a lower speed parallel data for each ofthe channels on path 179. Similarly, transmitter 180 may receive a lowspeed parallel data on path 198 and transmit a higher speed serial dataon path 186. In an embodiment, receiver 160 and transmitter 150 arerespectively implemented similar to receiver 170 and transmitter 180.However, as embodiments of receiver 170 and transmitter 180 can beimplemented to conform with OIF standards while implementing variousfeatures of the present invention, alternative embodiments of receiver160 and transmitter 150 may be implemented in a known way consistentwith OIF format.

Framer core logic 190 may receive parallel data corresponding tomultiple data channels on path 179 and convert the parallel data intocorresponding frames. The frames are provided to switch fabric 130 onpath 193. Similarly, framer core logic 190 may receive frames on path193, and converts the frames into parallel data corresponding tomultiple data channels on path 198.

As noted above, transmitter 150 receives the parallel data correspondingto multiple channels on path 145 and converts the parallel data of eachchannel into a serial data of corresponding channel along with a commonclock signal. Receiver 170 receives the serial data corresponding tomultiple channels on path 157 and converts the serial data into paralleldata corresponding to each channel. Transmitter 150 and receiver 170respectively transmit and receive multiple serial data channels on path157. The multiple serial data channels may be implemented as synchronouschannels sharing the same clock signal as a reference signal.

In general, each receiver-transmitter pair operates consistent withSFI-4 standard as noted above. However, various modifications can bemade to each of the receivers and transmitters independent of thecomponent on the other side. In particular, aspects of the presentinvention enables each component to use common clock signals in bothreception and transmission of data on the data channels. By using suchcommon clock signals, advantages such as reduction in electrical powerconsumption can be realized.

To enable the use of a common clock signal, the channels on thecorresponding side may need to remain synchronized to a common timereference. The manner in which the present invention enables suchsynchronization to be maintained is described below with severalexamples.

3. Method

FIG. 2 is a flowchart illustrating the details of a method by whichsynchronization may be maintained in various data channels according toan aspect of the present invention. The method is described withreference to FIG. 1 for illustration. However, the method can beimplemented in other embodiments without departing from the scope andspirit of the present invention, as will be apparent to one skilled inthe relevant arts based on the disclosure provided herein. The methodbegins in step 201 in which control passes to step 210.

In step 210, data streams (“receive data streams”.) are received on acorresponding number of receive channels. In step 220, each receive datastream is converted to a corresponding transmit stream in a formsuitable for further sending. If a receive data stream contains onlybits, the transmit stream is generated to contain multiple parallel dataelements. On the other hand, if a receive data stream contains paralleldata elements, the transmit data stream is generated to contain databits (forming serial data elements).

In step 230, each transmit data stream is transmitted on a correspondingone of multiple transmit channels. In step 240, a synchronization (sync)signal is generated. One of several approaches can be used to generatethe sync signal. An example approach for generating the sync signal isdescribed in a section below.

In step 260, the synchronization signal is used to ensure that all thechannels on a side containing the parallel data elements aresynchronized to a common time reference. While the steps are shown insequence, it should be understood that the steps can be performed inparallel. The steps of FIG. 2 are repeated, with the synchronizationsignal being generated at short intervals.

As a result, a common clock signal may be used associated with all theparallel data channels. In addition, another common clock signal may beused associated with the serial data channels as well due to the priorsynchronization. Several embodiments may be implemented using theapproach(es) of FIG. 2. Example embodiments are described first withreference to receiver 170 and then with reference to transmitter 180.

4. Receiver

FIG. 3 is a block diagram illustrating the details of receiver 170 in anembodiment of the present invention. Receiver 170 is shown containingserial to parallel converter blocks 320-1 through 320-16, and syncgenerator (SYNC8) 350. Each component is described in detail below.

For illustration, receiver 170 is shown receiving 16 independent serialdata channels 157-1 through 157-16 (all contained in path 157 of FIG. 1)and common clock signal 301. While the embodiments are described withreference to 16 channels for illustration, alternative embodiments canbe implemented with a different number of channels without departingfrom the scope and spirit of various aspects of the present invention,as will be apparent to one skilled in the relevant arts.

Common clock signal 301 represents the reference clock signal to whichthe received serial data channels 157-1 through 157-16 are synchronized.Common clock signal 301 may be generated based on a clock signalreceived from transmitter 150 along with the 16 serial data channels.

Sync generator 350 generates sync signal resynchzinta 352-1 and asimilar sync signal resynchzintb 352-2. The resynchzinta andresynchzintb signals may be identical signals and operate in similarmanner. By using different identical signals, the capacitive load onsync generator 350 is advantageously distributed among the signals.

The sync signals may be generated only when sync-enable signal 355 is ata logic high. Sync generator 350 also receives CLK signal 301 and RESETZ305 signals. The RESETZ signal initially resets sync generator 350 to aknown state. Common clock signal 301 is used to ensure that resynchzinta352-1 and resynchzintb 352-2 (resync signals) are consistently generatedat a specific phase relationship with clock signal 301.

The resync signals may be generated at a frequency determined by thenumber of bits in the parallel path of each of the 16 channels. Assumingeach parallel path 364-1 through 364-16 contains 8 bits, the resyncsignals may be generated in the form of pulses every (n×8)—cycles (where‘x’ represents multiplication and ‘n’ is an integer constant) of CLKsignal 301.

Serial to parallel converter blocks 320-1 through 320-16 respectivelyreceive the high speed serial data on channels 157-1 through 157-16, andsample the corresponding data bits according to CLK 301 signal. Serialto parallel converter blocks 320-1 through 320-16 respectively convertthe high speed serial data into parallel data, which is then provided onpaths 364-1 through 364-16.

In addition, each of serial to parallel converter blocks 320-1 through320-16 may generate clock signals (not shown) to provide time referenceto the corresponding parallel data. However, the clock signals may besynchronized to a common time reference using the resync signals. As aresult, one of the clock signals may be used as a common clock signals2pclkout 364-17 associated with all 16 parallel data channels 364-1through 364-16 (all paths 364-1 through 364-17 being contained in path179 of FIG. 1). Thus, the parallel data of all 16 channels on paths364-1 through 364-16 may be provided using s2pclkout 364-17 as a commontime reference clock. The RESETZ signal is used to reset all serial toparallel converter blocks 320-1 through 320-16 to a known state.

Serial to parallel converter blocks 320-1 through 320-8 also receiveresynchzinta 352-1 and blocks 320-9 through 320-16 receive resynchzintb352-2. The resynchzinta and resynchzintb signals are used to synchronizethe blocks that are out of sync with the common reference clocks2pclkout 364-17. Example embodiments of serial to parallel converterblocks 320-1 through 320-16 are described below with reference to FIG.4.

5. Serial to Parallel Converter

FIGS. 4A, 4B and 4C together represent a circuit diagram illustratingthe details of serial to parallel converter 320-1 in an embodiment ofthe present invention. However, the remaining serial to parallelconverter blocks 320-2 through 320-16 may also be implemented in asimilar manner. Serial to parallel converter 320-1 is shown containingsignaling circuit 440, serial shift register 450, sync counter 470, andparallel shift register 480. Each component is described below.

Serial to parallel converter 320-1 converts high speed serial datareceived on path 157-1 into 8-bit parallel data on paths 490-1 through490-8 (part of path 364-1 of FIG. 3). For illustration, serial toparallel converter 320-1 is implemented to provide 8-bit parallel data.However, alternative embodiments may be implemented with differentnumber of bits in parallel without departing from the scope and spiritof the present invention, as will be apparent to one skilled in therelevant arts based on the disclosure provided herein.

Continuing with exclusive reference to FIG. 4A, signaling circuit 440 isshown containing inverters 405, 407, 415, 456 and 457. NOR gate 410,complementary signal generators 420 and 445, buffer 430, and flip-flops449 and 455. The components operate to generate BUFCLK 425-1, BUFCLKZ425-2, BUFDIN 435, INTRESET 465 (internal reset). The components andoutput signals are described below in further detail.

Inverter 405 and NOR gate 410 operate to pass CLK signal 301 whenINTRESET 465 is at a low logical level. When INTRESET 465 is high, CLKsignal 301 is not passed through. Complementary signal generator 420receives (the double inverted) CLK signal 301 and generates BUFCLK 425-1and BUFCLKZ 425-2 signals. The BUFCLK 425-1 and BUFCLKZ 425-2 signalsare complement to each other (i.e., 180 degrees out of phase), but withtransitions occurring at the same time points. It may thus beappreciated that inverter 405, NOR gate 410 and complementary signalgenerator 420 together provide a delayed version of CLK signal 301 toserial shift register 450.

Buffer 430 receives serial data on path 157-1 and provides the delayeddata BUFDIN 435. Butter 430 is shown containing six inverters connectedin series and thus the output of buffer 430 is same as the input signalexcept with certain delay. Buffer 430 may be designed to provide thesame amount of delay as components 405, 410 and 420 in order to providethe received serial data on path 157-1 at the same time as CLK signal301 to serial shift register 450.

Inverters 407, 415, and 456, complementary signal generator 445, andflip-flops 449 and 455 operate to generate INTRESETZ 467, whichrepresents RESETZ signal 305 synchronized with CLK signal 301 to avoidmeta-stability. To achieve such a result, inverter 407 inverts theinverted CLK signal (generated by inverter 405) and provides the delayedCLK signal to complementary signal generator 445. Complementary signalgenerator 445 generates the complementary clock signals clkin 446 andclkinz 447, which are respectively connected to clk and clkz inputs offlip-flops 449 and 455.

Flip-flop 449 receives the inverted RESETZ signal from inverter 415 andclock signals (clkin and clkinz) derived from CLK 301, and provides theinverted and synchronized RESETZ signal to flip-flop 455. Flip-flop 455again synchronizes the inverted RESETZ signal with the clock signals(clkin and clkinz) and provides the synchronized RESETZ signal toinverter 456.

Inverter 456 inverts the inverted and synchronized RESETZ signal andprovides the synchronized RESETZ signal as INTRESETZ 467. INTRESETZsignal 467 is inverted by inverter 457 and provided as INTRESET 465.Thus, signaling circuit 440 provides CLK 301, RESETZ 305 and serial data157-1 respectively to serial shift register 450 as BUFCLK 425-1,INTRESET 465 and BUFDIN 435 with a desired timing relationship.

Serial shift register 450 receives BUFCLK (clock generated bycomplementary signal generator) 425-1, BUFCLKZ (inverted version ofBUFCLK) 425-2, BUFDIN 435, INTRESET (internal reset) 465. Serial shiftregister 450 may be implemented to operate at high frequency of theclock signals BUFCLK and BUFCLKZ.

Serial shift register 450 is shown containing eight flip-flops connectedin series. Each flip-flop contains two clock inputs, D-input, CLR inputand Q-output. Each flip-flop may be implemented in master-slaveconfiguration, which needs complementary clock signals. Thus, twocomplementary clock signals BUFCLK 425-1 and BUFCLKZ 425-2 (generated bycomplementary signal generator 420) are provided to reduce set up timeof the flip-flop. The two clock inputs of each flip-flop arerespectively connected to clock signals BUFCLK 425-1 and BUFCLKZ 425-2.

The D-input of the first flip-flop is connected to BUFDIN 435 and theD-input of remaining flip-flops are connected to Q-output of theprevious flip-flop. The CLR input of all flip-flops is connected toINTRESET 465.

In operation, all flip-flops may initially be reset to logic low byasserting INTRESET 465 signal. After resetting all the flip-flops, eightsuccessive bits of the serial data received on BUFDIN 435 are stored inthe eight flip-flops by the shift operations. The stored 8-bits areprovided on paths 458-1 through 458-8.

Continuing with reference to FIG. 4B, sync counter 470 generates divby8478 and divby8 z 479 clock signals, which represent CLK 301 divided by8, but re-synchronized with resynchzinta 352-1. Divby8 478 clock signalmay represent the common time reference clock signal s2pclkout 364-17(of FIG. 3) to provide parallel data on paths 490-1 through 490-8. Thetwo clock signals divbys and divby8 z are complements of each other.Sync counter 470 is shown containing flip-flop 475, NAND gate 476,complementary signal generator 477, five flip-flops F1, F2, F3, F4 andF5, inverter 474 and buffers B1 and B2. The operation of each componentis described below.

Flip-flop 475 synchronizes resynchzinta 352-1 to clkin 446 and clkinz447, and generates the synchronized signal on the Q-output. As may beappreciated, flip-flop 475 provides a delay to satisfy setup and holdtimes for resynchzinta signal 352-1 when the signal arrives at the inputof flip-flops F1-F5.

NAND gate 476 generates an output of high logical value when either theoutput of flip-flop 475 (i.e., re-timed resynchzinta 352-1) or INTRESETZ467 is of a low logical value, and an output of a low logical valueotherwise. Complementary signal generator 477 generates clr 471 whichequals the output of NAND gate 476. Complementary signal generator 477further generates prez 472, which represents an inverted version of clr471 with the same time reference.

Each of the flip-flops F1, F2, F3 and F4 contains inputs clk, clkz, D,clr and output Q. Flip-flop F5 contains inputs clk, clckz, D, prez andoutput Q. The inputs clk and clkz of all flip-flops are respectivelyconnected to clkin 446 and clkinz 447 signals. The clr input offlip-flops F1, F2, F3 and F4 is connected to clr signal 471 and prezinput of flip-flop F5 is connected to prez signal 472. The output ofeach flip-flop is connected to D-input of the next flip-flop except thatthe D-input of flip-flop F1. The D-input of flip-flop F1 is connected toinverted Q-output of flip-flop F4 through inverter 474.

Flip-flops F1, F2, F3, F4 and F5 and inverter 474 form a Johnson counterwith 8-states repeating for every eight clock cycles. A logical lowvalue of resynchzinta 352-1 causes clr 471 and prez 472 signals to behigh and low respectively, which clears Q-outputs (makes logic low) offlip-flops F1, F2, F3 and F4 and sets (makes logic high) flip-flop F5.The Q-output of flip-flops F1, F2, F3, F4 and F5 are respectivelyrepresented as Q1, Q2, Q3, Q4 and Q5. By denoting an output state inwhich (Q1 Q2 Q3 Q4 Q5=0 0 0 0 1) as state A, the Johnson counter attainsstate A once in every 8-clock cycles.

Buffer B1 inverts Q5 to generate divby8 signal 478. As Q5 stays high forfour consecutive clock cycles and low for four consecutive clock cycles,divby8 signal 478 operates with a period of eight cycles of CLK signal301. Buffer B1 may be implemented using inverters connected in sequence,as shown. Buffer B2 receives the output of flip-flop F1 (Q1) and isshown implemented with three inverters (similar to butter B1) connectedin series. Thus, buffer B2 inverts Q1 and provides the output divby8zsignal 479. As the output Q1 goes low once in every 8^(th) clock cycle,divby8z signal 479 goes high once in every 8^(th) cycle, and thusoperates as a complement of divby8 signal 478.

Due to reasons such as alpha particle hits or power supply glitches anddrifts, divby8 signal 478 of one or a few of the 16 serial-to-parallelconverter blocks 320-1 through 320-16 may not go low exactly once every8^(th) clock cycle of clkin signal 446. The manner in which suchout-of-synchronization signals may be re-timed to attain synchronizationis described again with reference to block 320-1 below.

It may be first appreciated that resynchzinta 352-1 goes low once inevery 8^(uh) (corresponding to 8-bits of parallel data on path 364-1)clock cycle (of CLK 301) causing clr 471 and prez 472 to go high. Thehigh state in turn causes the Johnson counter of flip-flops F1, F2, F3,F4 and F5 to change to state A (convention noted in the paragraphsabove). Therefore, resynchzinta signal 352-1 causes the Johnson counterto change to state A, which causes the output Q5 to go high andaccordingly the divby8 signal 478 goes low. For example, if resynchzinta352-1 goes low at clock cycles denoted by p, p+8, p+16, etc., then allthe channels operate synchronized starting from clock cycles denoted byp+1, (p+8)+1, (p+16)+1, respectively. Thus, the sync signal(resynchzinta 352-1) may cause the out-of-sync channel to be in syncwithout much latency.

However, resynchzinta signal 352-1 may not affect channels already insync. If serial to parallel converter 320-1 is already in sync, synccounter 470 may already reach state A independently when clr 471 isasserted. Thus, a channel which is already in sync may operate withoutbeing affected even if resynchzinta signal 352-1 is applied.

The sync signal to all sync counters in serial to parallel converterblocks 320-1 through 320-16 may be received substantially at the sametime and thus all channels which are out of sync may be synchronizedwithout much latency. The manner in which the divbys signal of channel 1and channel 2 changes with resynchzinta signal is illustrated insections below with reference to FIGS. 5A to 5C.

Now continuing with reference to FIG. 4C, parallel shift register 480receives divby8 478, divby8 z 479 signals and 8-bit serial data storedin serial shift register 450 on paths 458-1 through 458-8. Parallelshift register 480 converts the received high speed serial data into lowspeed parallel data, and provides the converted data bits on paths 490-1through 490-8 (forming path 364-1 of FIG. 3).

Parallel shift register 480 is shown containing eight flip-flops, witheach flip-flop containing clk, clkz and D-inputs, and Q-output. The clkand clkz inputs are respectively connected to divby8 z 479 and divby8478 signals and D-inputs of eight flip-flops are respectively providedwith a bit of 8-bit serial data on paths 458-1 through 458-8 (generatedin FIG. 4A). The Q-output of each flip-flop is connected to acorresponding buffer formed by two inverters connected in series. Theoutput of each buffer is provided on a corresponding one of paths 490-1through 490-8.

Parallel shift register 480 provides the parallel data on paths 490-1through 490-8 whenever it receives divby8 and divby8z clock signal. Thedivby8z signal goes high and divby8 goes low once every 8^(th) cycle ofCLK signal 301 as described above. Thus, 8-bits of high speed serialdata 157-1 are shifted into serial shift register 450 using high speedclock CLK 301. Parallel shift register 480 provides the 8-bit paralleldata on paths 490-1 through 490-8 using low speed clock divby8 478.

The divby8 and divby8z signals in serial to parallel converter blocks320-1 through 320-16 may be generated synchronous with the sync signals(resynchzinta or resynchzintb). However, the divby8 signal correspondingto only one of the blocks 320-1 through 320-16 may be provided ass2pclkout on path 364-17 to SERDES core logic 140. The manner in whichthe divby8 signal may be re-timed for synchronization with resynchzintasignal is illustrated below with reference to FIGS. 5A to 5C.

6. Divby8 Signal

FIGS. 5A, 5B and 5C are graphs together illustrating the details ofchanges in divby8 signal of channel1 (e.g., 157-1) and channel2 (e.g.,157-2) responsive to resynchzinta signal. FIGS. 5A to 5C illustrate onlythe divby8 signal of channel1 and channel2, however, all the remainingchannels may operate in similar manner.

FIG. 5A is a graph illustrating the details of change in divby8 signalof channel1 and channel2 when channel1 and channel2 are in sync (normaloperation). Lines 510, 520, 530 and 540 represent CLK, resynchzinta,divby8 of channel1 and divby8 of channel2 signals respectively. The CLKsignal changes periodically with respect to time as illustrated by line510. Line 520 representing the resynchzinta signal, which is generatedby sync generator 350 to synchronize the data channels that are out ofsync.

The resynchzinta signal is generated for a short interval, which goeslow once in every 8^(th) cycle of the CLK signal as represented by timepoints 5.15, 525 and 535 and remains low for one cycle of CLK signal. Innormal operation of receiver 170, the divby8 signal of channels 1 and 2transitions from a logic high to low once in every 8^(th) cycle of CLKsignal as represented by time points 515, 525 and 535, and accordinglyno re-synchronization is required.

FIG. 5B is a graph illustrating the details of change in divby8 signalof channel1 and channel2 with reference to CLK signal when channel1 goesout of sync (i.e., the divby8 transition occurs after the resynchzintapulse). Lines 550 and 555 respectively illustrate the divby8 signal ofchannel1 and channel2 before synchronisation. It can be observed thatline 550 is not making a transition from logic high to low at time point515 (corresponding to the falling edge of divby8 clock), reflecting anout-of-sync status.

Now, assuming that the resynchzinta signal is applied and goes low attime point 515, sync counter 470 is forced to switch to state A and thuscausing divby8 signal of channel1 to go low immediately in the samecycle of CLK signal 301 as illustrated by line 560. Line 555 ofchannel2, which is already in sync, may not change from its normaloperation. Thus, channel1, which is out of sync, may be re-synchronizedwith the resynchzinta signal.

FIG. 5C is a graph illustrating the manner in which divby8 signal isre-synchronized even in situations when the divby8 transition occursbefore the resynchzinta pulse. As may be observed from line 570, thedivby8 transitions can continue to occur before the resynchzinta,thereby requiring re-synchronization. The resynchzinta pulse attimepoint 515 causes the divby8 signal of channel1 to make a transitionexactly at every 8^(th) cycle of CLK signal as represented by line 580.Line 575 of channel2, which is already in sync, may not change from itsnormal operation.

Thus, channel1, which is out of sync, may be re-synchronized with theresynchzinta signal. The manner in which the sync signal (resynchzinta)is generated is described below with reference to FIG. 6.

7. Sync Generator

FIG. 6 is a circuit diagram illustrating the details of sync generator(sync8) 350 in an embodiment of the present invention. Sync generator350 receives CLK 301, sync-enable 355 and RESETZ 305 signals and maygenerate RESYNCHZINTA 352-1 and RESYNCHZINTB 352-2 signals. RESYNCHZINTA352-1 and RESYNCHZINTB 352-2 (resync signals) signals are periodicsignals of short interval, which repeats for every n×M cycles, wherein‘n’ represents an integer, ‘x’ represents multiplication, ‘M’ representsthe number of parallel bits generated by serial to parallel converterblocks 320-1 to 320-16. In an embodiment of the present invention, ‘n’and ‘M’ respectively equal 1 and 8.

Therefore, for illustration, sync generator 350 is implemented to repeatRESYNCHZINTA 352-1 and RESYNCHZINTB 352-2 signals for every 8 cycles. Inan embodiment, RESYNCHZINTA 352-1 and RESYNCHZINTB 352-2 makes atransition from a logic high to logic low for every 8^(th) cycle andstays low only for one cycle of CLK signal 301. The logical value ofRESYNCHZINTA 352-1 and RESYNCHZINTB 352-2 may change as . . .011111110111111011111110 . . . , which is also illustrated above by line520 of FIG. 5A. However, alternative embodiments may be implemented withseveral variations without departing from the scope and spirit of thepresent invention, as will be apparent to one skilled in the relevantarts based on the disclosure provided herein.

Sync generator 350 is shown containing inverters 610, 625, 661, 662,671, 672 and 673, NAND gates 615, 640 and 665, NOR gate 675,complementary signal generators 620 and 645, and flip-flops 650, 655,670 and 681, 682, 683, 684 and 685. Each component is described below.

Inverter 610 and NAND gate 615 operate to pass CLK signal 301 whensynchronized RESETZ 666 is at a high logical level. When synchronizedRESETZ 666 is low, CLK signal 301 is not passed through. Complementarysignal generator 620 receives (the double inverted) CLK signal 301 andgenerates CLKBUF 628 and CLKBUFZ 629 signals. CLKBUF 628 and CLKBUFZ 629are complement to each other, but with transitions occurring at the sametime points (i.e., out of phase by 180 degrees).

Inverters 625 and 661, NAND gate 640, complementary signal generator645, and flip-flops 650 and 655 operate to generate synchronized RESETZ666, which represents RESETZ signal 305 synchronized with CLK signal 301to avoid meta-stability. To achieve such a result, inverter 625 invertsthe inverted CLK signal (generated by inverter 610) and provides thedelayed CLK signal to complementary signal generator 645. Complementarysignal generator 645 generates the complementary clock signals inclk 646and inclkz 647, which are respectively connected to clk and clkz inputsof flip-flops 650 and 655.

NAND gate 640 inverts RESETZ 305 and provides the resulting RESET signalto D-input of flip-flop 650 when sync-enable 355 is high. Flip-flop 650receives the inverted RESETZ from NAND gate 640 and clock signals (inclk646 and inclkz 647) derived from CLK and provides the inverted andsynchronized RESETZ signal to flip-flop 655. Flip-flop 655 againsynchronizes the inverted RESETZ signal with the clock signals (inclk646 and inclkz 647) and provides the synchronized RESETZ signal toinverter 661.

Inverter 661 inverts the inverted and synchronized RESETZ signal andgenerates the synchronized RESETZ signal 666. Inverter 662 furtherinverts the synchronized RESETZ signal 666 and provides the resultingRESET signal on path 668, which is connected to clr input of flip-flops681, 682, 683, 684 and 685.

Flip-flops 681, 682, 683, 684 and 685, and NOR gate 675 form a modifiedJohnson counter, which repeats eight states for every eight consecutivecycles of CLK signal 301. Flip-flops 681, 682, 683, 684 and 685 containinputs clk, clkz, D, clr and output Q. The inputs clk, clkz and clr ofeach flip-flop are respectively connected to CLKBUF 628, CLKBUFZ 629 andRESETZ signal on path 668.

The Q-outputs of flip-flops 681, 682, 683, 684 and 685 are respectivelydenoted by Q0, Q1, Q2, Q3, and Q4. The Q-output of each flip-flop isconnected to D-input of the next flip-flop except the D-input offlip-flop F1. For example. Q0 is connected to D-input of flip-flop 682,Q1 is connected to D-input of flip-flop 683, etc. The D-input offlip-flop F1 is connected to NOR gate 675.

NOR gate 675 receives Q2. Q3 and Q4 and may provide the logical NOR ofQ2, Q3 and Q4 to D-input of flip-flop 681. NAND gate 665 receives Q1 andQ3 and provides the output to D-input of flip-flop 670. NAND gate 665may decode one of the eight states of the modified Johnson counter. Theeight states are described below with reference to FIG. 7.

When RESETZ 305 or sync-enable 355 is low, flip-flops 681, 682, 683, 684and 685 are cleared and hence the output ‘Q0 Q1 Q2 Q3 Q4’ may be ‘0 0 00 0’, which is represented by state 1 in FIG. 7. When RESETZ 305 ishigh, the modified Johnson counter starts counting and thus the outputis represented by other seven states (states 2, 3, 4, 5, 6, 7 and 8).The eight states are repeated for every eight clock cycles.

NAND gate 665 may decode the outputs Q1 and Q3 to generate resynchzinta352-1 and resynchzintb 352-2, which may go low for every eight cycles.The output of NAND gate 665 is low only for state 5 and is high for allother states. Thus, the output of NAND gate 665, which may representresynchzinta 352-1 and resynchzintb 352-2 signals, transitions from highto low for every eight cycles and remains low only for one cycle (in thesteady state).

Flip-flop 670 synchronizes the output of NAND gate 665 to INCLK 646 (andINCLKZ 647). Inverter 671 inverts the Q-output of flip-flop 670, andinverters 672 and 673 further inverts the output of inverter 671. Theoutputs of inverters 672 and 673 are respectively provided asresynchzinta 352-1 and resynchzintb 352-2. As may be appreciated,resynchzinta 352-1 and resynchzintb 352-2 are identical, and provided ontwo different paths to drive multiple serial to parallel converterblocks.

The synchronization signals thus generated are used to synchronize thevarious data channels in receiver 170 as described above. As alsodescribed above, the data of some of the channels is generated bytransmitter 150, which can be implemented similar to transmitter 180.The manner in which transmitter 180 is implemented in an embodimentaccording to the present invention is described below with reference toFIG. 8.

8. Transmitter

FIG. 8 is a block diagram illustrating the details of transmitter 180 inan embodiment of the present invention. Transmitter 180 is showncontaining parallel to serial converter blocks 810-1 through 810-16,phase locked loop (PLL) 830 and sync generator (SYNC8) 850. Eachcomponent is described in detail below.

For illustration, transmitter 180 is shown containing 16 independentdata channels 198-1 through 198-16 (all contained in path 198 of FIG. 1)and common byte clock 815. While the embodiments are described withreference to 16 channels for illustration, alternative embodiments canbe implemented with a different number of channels without departingfrom the scope and spirit of various aspects of the present invention,as will be apparent to one skilled in the relevant arts by reading thedisclosure provided herein.

PLL 830 may generate clock signals 801, 802 and 803, which arerespectively provided to parallel to serial converter blocks 810-1through 810-8, 810-9 through 810-16, and sync generator 850. The threeclock signals are identical but may be generated as such merely todistribute the capacitive load on PLL 830. PLL 830 may be implemented ina known way.

Common byte clock 815 represents a reference clock signal using whichdata is received on channels 198-1 through 198-16. A byte of data may bereceived on each rising edge of common byte clock 815, and thus all thereceive channels are synchronized to common byte clock 815. Byte clocksignal 815 may be generated by dividing clock signal 801 by eight.

Each of parallel to serial converter blocks 810-1 through 810-16 maygenerate byte clock signals (not shown) to provide time reference toreceive the corresponding parallel data. However, the byte clock signalsmay be synchronized to a common time reference using the resync signals.As a result, one of the byte clock signals may be used as a common clockassociated with all 16 parallel data channels 198-1 through 198-16.Thus, common byte clock 815 may be generated by one of the parallel toserial converter blocks 810-1 through 810-16, but used by all the blocksto receive the corresponding data bytes. Similarly, clkout 825 may alsobe venerated by one of the blocks, but used by all other blocks whiletransmitting the data on the respective serial communication channels.

Sync generator 850 may generate resynchzinta 831-1 and resynchzintb831-2, which are similar to resynchzinta 352-1 and resynchzintb 352-2.Sync generator 850 may be implemented similar to sync generator 350,which is described above.

Each of the parallel to serial converter blocks 810-1 through 810-16converts the respective low speed parallel data into a high speed serialdata, and provides the converted data as a serial communication channelon the respective path 186-1 through 186-16. The high speed serial dataof all 16 channels on paths 186-1 through 186-16 may be provided usingclkout 825 as a common clock signal.

Parallel to serial converter blocks 810-1 through 810-8 also receiveresynchzinta 831-1 and blocks 810-9 through 810-16 receive resynchzintb831-2. The resynchzinta and resynchzintb signals are used to synchronizethe blocks that are out of sync. Example embodiments of parallel toserial converter blocks 810-1 through 810-16 are described below withreference to FIGS. 9A-9C.

9. Parallel to Serial Converter

FIGS. 9A, 9B and 9C together represent a circuit diagram illustratingthe details of parallel to serial converter 810-1 in an embodiment ofthe present invention. However, the remaining parallel to serialconverter blocks 810-2 through 810-16 may also be implemented in asimilar manner. Parallel to serial converter 810-1 is shown containingsignaling circuit 910, shift register 940 and sync counter 980. Eachcomponent is described below.

Continuing with exclusive reference to FIG. 9A, signaling circuit 910 isshown containing inverters 905, 907, 915, 930 and 932, NAND gate 935,complementary signal generators 912 and 937, and flip-flops 920 and 925.The components operate to generate CLKIN 938, CLKINZ 939 and CLR 934.The components and output signals are described below in further detail.

Inverter 905 and NAND gate 935 operate to pass CLK signal 801 whenINT-RESETZ 931 is at a high logical level (i.e., when no reset isrequested). When INT-RESETZ 931 is low, CLK signal 801 is not passedthrough. Complementary signal generator 937 receives (the doubleinverted) CLK signal 801 and generates CLKIN 938 and CLKINZ 939 signals.CLKIN 938 and CLKINZ 939 signals are complement to each other, but withtransitions occurring at the same time points (i.e., 180 degreesout-of-phase).

Inverters 907, 915, and 930, complementary signal generator 912, andflip-flops 920 and 925 operate to generate INT-RESETZ 931, whichrepresents RESETZ signal 902 synchronized with CLK signal 801 to avoidmeta-stability. To achieve such a result, inverter 907 inverts theinverted CLK signal and provides the delayed CLK signal to complementarysignal generator 912. Complementary signal generator 912 generates thecomplementary clock signals CLKI 913 and CLKIZ 914, which arerespectively connected to clk and clkz inputs of flip-flops 920 and 925.

Flip-flop 920 receives the inverted RESETZ signal from inverter 915 andclock signals (CLKI and CLKIZ) derived from CLK 801 and provides theinverted and synchronized RESETZ signal to flip-flop 925. Flip-flop 925again synchronizes the inverted RESETZ signal with the clock signals andprovides the resulting clock signal to inverter 930.

Inverter 930 inverts the inverted and synchronized RESETZ signal andprovides the synchronized RESETZ signal as INT-RESETZ 931. INT-RESETZ931 is inverted by inverter 932 and provided as CLR signal 934. Thus,signaling circuit 910 provides CLK 801 and RESETZ 902 respectively asCLKIN 938 and CLR 934 with a desired timing relationship to shiftregister 940.

Continuing with reference to FIG. 9B, sync counter 980 is showncontaining flip-flop 965, NAND gate 970, complementary signal generator975, flip-flops 960-1, 960-2, 960-3 and 960-4, inverters 977, 982 and984, and buffers 986 and 988. The components operate to generateBYTECLOCK 815, SELECT 991 and SELECTZ 992, which are all resynchronizedwith resynchzinta 831-1 as described below.

Flip-flop 965 synchronizes resynchzinta 831-1 to CLKI 913 and CLKIZ 914signals, and generates the synchronized signal on the Q-output. As maybe appreciated, flip-flop 965 provides a delay to satisfy setup and holdtimes for resynchzinta signal 831-1 when the signal arrives at the inputof flip-flops 960-1 through 960-4.

NAND gate 970 generates an output of high logical value when either theoutput of flip-flop 965 (i.e. re-timed resynchzinta 831-1) or INT-RESETZ931 is of a low logical value, and an output of a low logical valueotherwise. The output of NAND gate 970 thus contains a logical highvalue when flip-flops 960-1 through 960-4 need to be reset.

Complementary signal generator 975 generates clear (CLRI) which equalsthe output of NAND gate 970. Complementary signal generator 975 furthergenerates preset (PREZI) signal, which represents an inverted version ofCLRI with the same time reference.

Flip-flops 960-1, 960-2, 960-3 and 960-4 contain inputs clk, clckz, D,clr and output Q. The inputs clk and clkz of all flip-flops arerespectively connected to CLKI 913 and CLKIZ 914 signals. The clr inputof all flip-flops is connected to CLRI signal generated by complementarysignal generator 975. The output of each flip-flop is connected toD-input of the next flip-flop except the D-input of flip-flop 960-1. TheD-input of flip-flop 960-1 is connected to inverted Q-output offlip-flop 960-4 through inverter 977.

Flip-flops 960-1, 960-2, 960-3 and 960-4 and inverter 977 form a Johnsoncounter with 8-states (shown in FIG. 10) repeating for every eight clockcycles. When resynchzinta 831-1 is low, that causes CLRI to be high,which clears Q-outputs (makes logic low) of flip-flops 960-1, 960-2,960-3 and 960-4. The Q-output of flip-flops 960-1, 960-2, 960-3 and960-4 are respectively represented as Q1, Q2, Q3 and Q4. The eightstates shown in FIG. 10 would repeat during every successive eight clockcycles unless reset again CLRI signal.

Inverter 982 inverts the output Q1 and the inverted output is providedto both NAND gate 985 and inverter 984. The output of inverter 984 isprovided as BYTECLOCK 815, which would remain in a low state for fourconsecutive clock cycles and in a high logical state in the subsequentfour consecutive clock cycles. Thus, the BYTECLOCK is generated as a lowspeed clock having a frequency of one eighth the frequency of CLK signal801.

NAND gate 985 performs a NAND operation of Q2 and inverted Q1, andprovides the output to buffers 986 and 988. The output of NAND gate 980is low only for state 6 and is high for all other states as may beappreciated by examining FIG. 10. Thus, the output of NAND gate 985 isat low logical level for only one clock cycle, and in a high logicallevel during the remaining 7 clock cycles.

Buffer 986 is shown containing contain three inverters connected inseries, and thus inverts the output of NAND gate 985 to generate SELECT991. Thus. SELECT signal 991 would be at a high logical level in onlyone of the eight clock cycles. On the other hand, buffer 988 containingonly two inverters, generates SELECTZ 992 which remaining at a lowlogical value in only one of the eight clock cycles. The SELECT signalmay be used to load the low speed parallel data on path 198-1 into shiftregister 940 once every cycle of BYTECLOCK 815.

The manner in which BYTECLOCK 815, SELECT 991 and SELECTZ 992 aresynchronized using the resynchzinta 831-1 is described below.

It may be first appreciated that resynchzinta 831-1 signal goes low oncein every 8^(th) clock cycle causing CLRI signal to go high. The highstate in turn causes the Johnson counter of flip-flops 960-1 through960-4 to reset to all zeroes state. Therefore, resynchzinta signal 831-1causes the Johnson counter to be reset to all-zeroes state. Thus, thesync signal (resynchzinta) causes the out of sync channel 320-1 to be insync without any latency.

However, resynchzinta signal 831-1 may not affect channels which arealready in sync. If parallel to serial converter 810-1 is already insync, sync counter 980 may have already reached all zeroes independentlywhen CLRI is asserted. Thus, a channel which is already in sync operateswithout being affected even if resynchzinta signal 831-1 is applied.

The sync signal to all sync counters in parallel to serial converterblocks 810-1 through 810-16 may be received substantially at the sametime and thus all channels which are out of sync may be synchronized atthe same time and without substantial latency (one clock cycle in theabove examples).

Now, continuing with reference to FIG. 9C, shift register 940 receivesSELECT 991, SELECTZ 992, CLKIN 938, CLKINZ 939, CLR 934 signals and8-bit parallel data 198-1. Shift register 940 converts the received lowspeed parallel data into high speed serial data, and provides theconverted data bits on path 186-1 (contained in path 186 of FIG. 1).

Shift register 940 contains eight scan flip-flops 950-1 through 950-8and each scan flip-flop may contain clk, clkz, s, sz, A, B, and clrinputs, and Q-output. The clk and clkz inputs are respectively connectedto CLKIN 938 and CLKINZ 939 signals. The s and sz inputs arerespectively connected to SELECT 991 and SELECTZ 992 signals and B-inputof each scan flip-flop is connected to the corresponding bit of 8-bitparallel data on path 198-1. The A-input of each scan flip-flop isconnected to Q-output of the previous scan flip-flop except scanflip-flop 950-11. Tie-off cell 945 provides input to A-input of scanflip-flop 950-1, and is set to a pre-determined logical value (e.g., 0).

The Q-output of flip-flop 950-8 is connected to buffer 957, which maycontain two inverters connected in series. The output of buffer 957 maybe provided as serial data DOUT 186-1. Buffer 955 may receive CLKIN 938,which may contain two inverters connected in series. Buffer 955 mayprovide the output as high speed clock, CLKOUT 825.

Each scan flip-flop generally operates as a combination of a multiplexerand a flip-flop. When SELECT signal 991 is high once every eight cycles,the scan flip-flops load the parallel data into shift register 940.Then, when SELECT signal 991 is low, shift register 940 shifts the 8-bitparallel data out on path 186-1. Thus, the parallel data on path 198-1is converted into the serial data on path 186-1.

From the above, it may be readily appreciated that resynchzinta signal831-1 may synchronizes SELECT 991 and BYTECLOCK 815 signals, which maybe used to convert the low speed parallel data 198-1 into serial data186-1. Thus, parallel to serial converter 820-1 may be synchronized ifit is out of sync.

10. Conclusion

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. Thus, the breadth and scope of thepresent invention should not be limited by any of the above describedexemplary embodiments, but should be defined only in accordance with thefollowing claims and their equivalents.

1-37. (canceled)
 38. A receiver block comprising: a synchronizationgenerator generating a sequence of synchronization signals with a shortinterval between successive ones of said sequence of synchronizationsignals; and a plurality of converter blocks receiving each of aplurality of sequences of serial data elements on a corresponding one ofa plurality of serial data channels, said plurality of converter blocksconverting each of said plurality of sequences of serial data elementsto a corresponding one of a plurality of sequences of parallel dataelements, said plurality of converter blocks sending each of saidplurality of sequences of parallel data elements on a corresponding oneof a plurality of parallel data channels; and said plurality ofconverter blocks receiving said sequence of synchronization signals andensuring that said plurality of parallel data channels are synchronizedwith a first common clock signal in response to each of said sequence ofsynchronization signals such that all of said sequences of parallel dataelements are sent on said plurality of parallel data channels using saidfirst common clock signal.
 39. The receiver block of claim 38, whereinsaid plurality of converter blocks receive a second common clock signalassociated with said plurality of serial data channels, wherein saidsecond common clock signal provides a common reference for saidplurality of serial data channels.
 40. The receiver block of claim 39,wherein each of said parallel data elements comprises a byte containing8 bits, such that said sequence of synchronization signals are generatedperiodically with a period of eight times the period of said secondcommon clock signal, and wherein each of said sequence ofsynchronization signals comprises a pulse.
 41. The receiver block ofclaim 39, wherein a first converter block is contained in said pluralityof converter blocks, said first converter block comprising: a serialshift register receiving a plurality of bits on said serial datachannel; and a parallel register containing a plurality of memoryelements, said plurality of bits being loaded into said plurality ofmemory elements from said serial shift register at a time pointspecified in relation to said sequence of synchronization signals, saidplurality of bits being loaded into said plurality of memory elements togenerate a corresponding one of said parallel data elements.
 42. Thereceiver block of claim 41, wherein said first converter block comprisesa sync counter generating said first common clock signal synchronizedwith said sequence of synchronization signals, wherein said first commonclock signal has a frequency of 1/Number, wherein Number equals a numberof bits in each of said parallel data elements.
 43. The receiver blockof claim 42, wherein said first converter block comprises a signalingcircuit receiving said second common clock signal and generates acomplement of said second common clock signal, wherein said secondcommon clock signal and said complement of said second common clocksignal are out-of-phase by 180 degrees, wherein said serial shiftregister is coupled to receive said second common clock signal and saidcomplement of said second common clock signal.
 44. The receiver block ofclaim 43, wherein said signaling circuit comprises a buffer to delaysaid plurality of bits such that said plurality of bits are provided ata same time reference as said second common clock signal and saidcomplement of said second common clock signal to said serial shiftregister.
 45. The receiver block of claim 44, wherein said signalingcircuit further comprises: a first complementary signal generatorreceiving said second common clock signal, and generating a complementof said second common clock signal along with said second common clocksignal, which are out-of-phase by 180 degrees; a first flip-flopreceiving said second common clock signal, complement of said secondcommon clock signal and a reset signal, said first flip-flipsynchronizing said reset signal to said second common clock signal togenerate a first flip-flop output; a first inverter inverting said firstflip-flop output to generate a first inverter output; a first NOR gateperforming a logical NOR operation of said first flip-flop output and aninverted version of said second common clock signal to generate a firstNOR output; and a second complementary signal generator receiving saidfirst NOR output and generating said second common clock signal and saidcomplement of said second common clock signal.
 46. The receiver block ofclaim 45, wherein said sync counter comprises: a sequence of flip-flopsconnected in series, wherein an inverted version of an output of one ofsaid sequence of flip-flops is coupled as an input to a data input of afirst one of said sequence of flip-flop to form a modified Johnsoncounter; a second flip-flop synchronizing said sequence ofsynchronization signals to said second common clock signal to generate asecond flip-flop output; and a second NAND gate performing a logicalNAND operation of said second flip-flop output and said first inverteroutput to generate a second NAND output, wherein said second NAND outputis used to clear some of said sequence of flip-flops of said modifiedJohnson counter, and a complement of said second NAND output is used toclear another one of said sequence of flip-flops, wherein an output of alast one of said sequence of flip-flops is provided as said first commonclock signal.
 47. The receiver block of claim 44, wherein saidsynchronisation generator generates said sequence of synchronizationsignals with a frequency of [1/Number] of a frequency of said secondcommon clock signal, wherein Number equals a number of bits in each ofsaid parallel data elements.
 48. The receiver block of claim 38, whereinsaid synchronization generator generates a plurality of sequences ofsynchronization signals, wherein a first one of said plurality ofsequences of synchronization signals is provided to some of saidplurality of converter blocks and a second one of said plurality ofsequences of synchronization signals is provided to some other ones ofsaid plurality of converter blocks, wherein said plurality of sequencesof synchronization signals comprises said sequence of synchronizationsignals. 49-58. (canceled)
 59. A device comprising: a core logic block;a receiver block; a synchronization generator generating a sequence ofsynchronization signals with a short interval between successive ones ofsaid sequence of synchronization signals; and a plurality of converterblocks receiving each of a plurality of sequences of parallel dataelements on a corresponding one of a plurality of parallel data channelsfrom said core logic block, each of said plurality of converter blocksconverting a corresponding one of said plurality of sequences ofparallel data elements to a corresponding one of a plurality ofsequences of serial data elements, said plurality of converter blockssending each of said plurality of sequences of serial data elements on acorresponding one of a plurality of serial data channels to saidreceiver block, said plurality of converter blocks receiving saidsequence of synchronization signals and ensuring that said plurality ofparallel data channels are synchronized to a common time reference inresponse to each of said sequence of synchronization signals such that afirst common clock signal is used to receive all of said plurality ofsequences of parallel data elements on said plurality of parallel datachannels.
 60. The device of claim 59, wherein said plurality ofconverter blocks use a second common clock signal associated with saidplurality of serial data channels, wherein said plurality of serial datachannels are synchronized with said second common clock signal.
 61. Thedevice of claim 60, wherein each of said parallel data elementscomprises N bits, wherein N represents an integer, wherein said shortinterval equals M×N of a clock period of said second common clocksignal, wherein M also represents an integer and ‘x’ represents amultiplication operation.
 62. The device of claim 61, wherein each ofsaid parallel data elements comprises a byte containing 8 bits, and Mequals 1, such that said sequence of synchronization signals aregenerated periodically with a period of eight times the period of saidsecond common clock signal.
 63. The device of claim 62, wherein each ofsaid sequence of synchronization signals comprises a pulse.
 64. Thedevice of claim 60, wherein a first converter block is contained in saidplurality of converter blocks, said first converter block comprising ashift register converting each of said parallel data elements into aplurality of serial data elements, said shift register loading each ofsaid parallel data elements at a time point specified in relation to acorresponding one of said sequence of synchronization signals, saidshift register shifting a loaded parallel data element to generatecorresponding said plurality of serial data elements, wherein saidplurality of serial data elements are comprised in a correspondingsequence of serial data elements.
 65. The device of claim 64, whereinsaid first converter block further comprises a sync counter generating aselect signal synchronized with said sequence of synchronizationsignals, wherein said select signal specifies said time point to loadeach of said parallel data elements in said shift register.
 66. Thedevice of claim 65, wherein said sync counter generates said firstcommon clock signal synchronized with said sequence of synchronizationsignals, said first common clock signal providing a time reference toreceive said plurality of sequences of parallel data elements, whereinsaid first common clock signal has a frequency of [1/Number] of afrequency of said second common clock signal, wherein Number equals anumber of bits in each of said parallel data elements.
 67. The device ofclaim 66, wherein said second common clock signal provides a common timereference signal for said plurality of serial data channels.
 68. Thedevice of claim 67, further comprises: a PLL (phase lock loop)generating a PLL clock signal; and a signaling circuit passing said PLLclock signal as said second common clock signal when a reset signal isnot received.
 69. The device of claim 68, wherein said signaling circuitgenerates said second common clock signal and a complement of saidsecond common clock signal, which are out-of-phase by 180 degrees,wherein said shift register is coupled to receive said second commonclock signal and said complement of said second common clock signal. 70.The device of claim 69, wherein said signaling circuit furthersynchronizes said reset signal to said PLL clock signal to generate aclear signal, wherein said clear signal causes said shift register to becleared to all zeros state.
 71. The device of claim 70, wherein saidsignaling circuit comprises: a first complementary signal generatorreceiving said PLL clock signal, and generating a complement of said PLLclock signal along with said PLL clock signal, which are out-of-phase by180 degrees; a first flip-flop receiving said PLL clock signal,complement of said PLL clock signal and said reset signal, said firstflip-flip synchronizing said reset signal to said PLL clock signal togenerate a first flip-flop output; an inverter inverting said firstflip-flop output; a first NAND gate performing a logical NAND operationof an inverted version of said first flip-flop output and an invertedversion of said PLL clock signal to generate a first NAND output; and asecond complementary signal generator receiving said first NAND outputand generating said second common clock signal and said complement ofsaid second common clock signal.
 72. The device of claim 71, whereinsaid sync counter comprises: a sequence of flip-flops connected inseries, wherein an inverted version of an output of a last one of saidsequence of flip-flops is coupled as an input to a data input of a firstone of said sequence of flip-flops to form a modified Johnson counter; asecond flip-flop synchronizing said sequence of synchronization signalsto said PLL clock signal to generate a second flip-flop output; a secondNAND gate performing a logical NAND operation of said second flip-flopoutput and said inverted version of said first flip-flop output togenerate a second NAND output, wherein said second NAND output is usedto clear said modified Johnson counter; and a third NAND gate performinga logical NAND operation of two of the outputs of said sequence offlip-flops to generate said select signal.
 73. The device of claim 72,wherein an output of one of said sequence of flip-flops is provided assaid first common clock signal.
 74. The device of claim 68, wherein saidsynchronisation generator generates said sequence of synchronizationsignals with a frequency of [1/Number] of a frequency of said PLL clocksignal, wherein Number equals a number of bits in each of said paralleldata elements.
 75. The device of claim 59, wherein said synchronizationgenerator generates a plurality of sequences of synchronization signals,wherein a first one of said plurality of sequences of synchronizationsignals is provided to some of said plurality of converter blocks and asecond one of said plurality of sequences of synchronization signals isprovided to some other ones of said plurality of converter blocks,wherein said plurality of sequences of synchronization signals comprisessaid sequence of synchronization signals. 76-87. (canceled)